In an exhaust passage of an engine, a catalyst device for purifying an exhaust gas is disposed in general. A catalyst carried by the catalyst device does not exert a favorable catalytic function at a temperature less than an activation temperature and thus, a warm-up operation for raising a temperature of the catalyst to the activation temperature early is needed at start of the engine. As a method of the warm-up operation, there is a method of raising the temperature of the catalyst by raising a temperature of the exhaust gas by retarding ignition timing. Moreover, in such warm-up operation, in order to ensure favorable ignitability even in a state where the ignition timing is retarded, a so-called stratified charge combustion in which spark ignition is performed in a state where fuel spray is concentrated in the vicinity of an ignition plug is performed in some cases.